Detectives are to fly out to Guantanamo Bay to interview a British man over new torture claims against MI5.

Scotland Yard has asked the US authorities for permission to visit the 43-year-old British detainee who alleges that an MI5 officer was present when he was badly assaulted by a team of interrogators.

Shaker Aamer, the last remaining Briton at the US naval base in Cuba, has been held without trial for more than ten years after his capture in Afghanistan in 2001.

His allegations are the most serious to be levelled at the Security Service and include claims that a British interrogator was present when Mr Aamer’s head was repeatedly banged against a wall.

Previous cases against MI5 and MI6, the Secret Intelligence Service, have only included allegations that British officers sent intelligence to their US counterparts to assist in the interrogation of UK suspects held in unlawful detention.